Temperature regulating system



April 1939- I H. R. cRAed 2,155,256

TEMPERATURE REGULATING SYSTEM Filed Sept. 10, 1936 Inventor:

Harry F? .cvago;

His ttorrley for circulating the Patented Apr. 18, 1 939 UNITED STATES TEMPERATURE R EGULATING SYSTEM Harry R. Crago, Caldwell, N. J., assignor to General Electric Company, a corporation of New York Application september 10, 1936, Serial No. 100,119

. 13 Claims.

My invention relates to temperatifi'eregulating systems and more particularly to systems of the type in which the temperaturechanging means are controlled by independent thermal responsive means.

Dual thermostat control of heating and cooling means to maintain the temperature of an enclosed space within predetermined limits the year around has been used for reasons of economy, simplicity of the control and to insure dependable operation. Controls of this nature function properly when the thermal responsive means are non-adjustable or are adjusted to operate at different temperatures, as they are under normal operating conditions. However, adjustable thermal responsive means are desirable, if not necessary, in most installations and their use creates a possibility that they maybe adjusted to function at the same temperature and thereby simultaneously place in operation both heating and cooling means.

It is an object of my-invcntion to provide a new and improved dual thermostat control system in which simultaneous operation of. both temperature changing means is prevented.

More particularly it is an object of my invention to provide a control system in which the thermal responsive means controlling the heating means takes precedence when both thermal responsive means are adjusted to operate at the same temperature or in the same temperature range.

Another object of my invention is to so correlate the dual thermostat control with the means at exchange medium through the space that the irculating means is rendered operative only when the temperature of the medium reaches a predetermined value upon a call for heat and immediately upon a call for cooling.

This last mentioned aspect of my present invention is an improvement over the invention disclosed in my copending application, Serial No. 83,921, filed June 6, 1936. In this application is disclosed an arrangement in which a single thermal responsive means located in the space controls either the heating or cooling means, depending on which of these has been selected for operation. The air circulating means is operated intermittently in response to variations in space temperature and or the heat exchange medium' when heating means is selected for operation and continuously when the cooling means is selected for operation.

Other objects of my invention will become apparent from the ensuing description taken in conjunction with the accompanying drawing in which is set forth for the purpose of illustration the details of arrangement.

The single figure of the drawing shows diagrammatically air conditioning apparatus de- 5 signed for year around operation and illustrates schematically a control system therefor embodying the features of the present invention.

Referring to the figure, reference numeral l0 designates a space such as a room, building or the like, to which the conditioning medium, preferably air, is to be supplied. The air is supplied to the space by an air conditioner ll preferably located without said space and provided with the "usual recirculated air duct l2, a fresh air duct l5 l3 and a discharge duct II. The proportions of fresh and recirculated air may be controlled by dampers I5 and H5 in the recirculated and fresh air ducts, respectively. These may be controlled either manually or automatically in response to 2 indoor or outdoor temperature conditions. The conditioner is also provided with a fan l8 positioned in the discharge duct and driven by an electric motor l9, controlled in a manner hereinafter to be described, for circulating the air 2 through the space. The air drawn through the conditioner may be conditioned by suitable heating, cooling and humidiiying means forming part of the conditioner.

The cooling means consists of the usual me- 30 chanical refrigerating apparatus comprising an evaporator, compressor, condenser, liquid receiver and expansion valve. The evaporator is connected by a conduit 2| to the suction side of a compressor 22. The high pressure side of the 5 compressor is connected by conduit 23 to a con-- denser 24 which may be cooled in any suitable manner. The condenser in turn is connected to a liquid receiver 25 and the latter is connected through conduit '26 to a thermostatically con- 40 trolled expansion valve 21 controlling the refrigerant new to the evaporator. The compressor itself is driven by a suitable prime mover such as an electric motor 28, also controlled in response to temperature variations in the enclosure in a manner hereinafter to be described. 4

To properly humidity the air supplied to the space during seasons when heating is required,

' I have provided a humidifying apparatus 30.

is illustrated as being of the wire -screenf'"type so but may be of any other desirable construction. Water is supplied to the humidifier through a conduit 3| under the control of a valve having a spring biased. operating arm 33 and adapted to be moved from closed to open position, and vice 66 'tion of suitable electrical control means 38 and likewise to decrease the supply of heat upon the deenergization thereof. The energization of the control means is also under the control of thermal responsive means located within the space being conditioned as will be described more in detail later.

My invention is not directed to any particular type of temperature changing or humidifying means. It is obvious to those skilled in the art that instead of using heating and cooling means of the types illustrated, I may equally well use hot and cold water and control the supply thereof detail later, is

to the heat exchanger units in the conditioner by suitable electrically operated valves in the supply conduits.

The control, which will be described in greater such that when the temperature within the enclosure l0 falls below a value at which it is desirable to place the heating means into operation, the latter will be placed under the control of thermal responsive'means 4| positioned in the enclosure. As brought out generally heretofore, the air circulating means is not only under the control of the thermal responsive means 4| but is also under the control of a second thermal responsive means.42, called a heat exchanger thermostat, positioned adjacent. to or in the near vicinity of the heating means 35. According to this arrangement the circulating means is operated onlyupon a call for heat and when the temperature of the air flowing past the second thermal responsive means is above a predetermined value. The cooling means is under the control of a third thermal responsive means 43 also positioned within the enclosure l8. When cooling is called for by the last mentioned thermal responsive means the air circulating meansis placed into operation simultaneously with the cooling means.

The control of the humidifying means within the conditioner issimilar to that disclosed and claimed in my application for Letters Patent, Serial No. 83,921, referred to previously. Briefly, the control is such that the humidifying means may be placed into operation only during those periods when the heating means is in operation and the fan has also been placed in operation. When these conditions obtain the supply of water to the humidifier will be under the control of a humidostat 44 positioned either within the enclosure or in the return duct from the enclosure and responsive to humidity variations therein.

The'detaiied description of thevarious electrical circuits whereby the control outlined briefly above functions-will now be given. The

' .various'controls and the electrical apparatus of the system are provided with, electrical energy from a pair of supplyconductors 45 which may beconnected to a suitable source of energy by meansof a manually operable switch-48. The

thermal responsive means 4| and 43, which will hereinafter'be referred to as the heating thermo'stat and cooling thermostat, respectively, are

thermostat 42. Element nected by a conductor 88.--to a conductor 89, one

. ductor 9| leads to one of the'conductors provided with low voltage energy through transformers 41 and 48, respectively. The secondary winding of transformer 41 is connected by means of conductors 49 and 50 to a pair of adjustably mounted contacts 5| and 52 associated with the thermal responsive element 53 of the heating thermostat 4|. Thermal responsive element 53, which is illustrated as being of the bi. metallic type, is connected by. means of a conductor 54 to relay 55 and a normally open switch 56 controlled by said relay. Switch 55 controls a holding circuit for relay 55 extending from conductor 54 to a conductor 51 connected to the secondary winding of the transformer. Relay 55 is also adapted to actuate a second switch 58 operable from engagement with a first contact 58 into engagement with a second contact 68. Switch member 58 is connected to the source of energy by a conductor 8|. When the switch is in engagement with contact 59 an energizing circuit is conditioned for closure by the cooling be explained more fully thermostat 43, as will hereinafter, and when the switch member is actuated into engagement with contact a circuit including conductor 6|, an electrical control device ductors 63 through which power is supplied to -the electrical control means 38 of the furnace is closed. Relay 52 is adapted to actuate a pair of switches 54 and 65, the former connecting such as relay 62, and one of conthe electrical control means 38 of furnace 31 to with that of the heating thermostat 4|. Conductors 81 and 58 lead from the terminals of the secondary winding of the transformer to adjustably mounted contacts 59 and 18 associated with the thermal responsive element 1| of the thermostat. The latter is connected by a conductor 12 to a relay 13 and to a switch 14 adapted when actuated to itsclosed position upon energization of relay 13 to close a holding'circuit for the relay. Relay 13 is also adapted to actuate a, second switch 15 into and out of engagement with a contact 15. When the switch is in engagement with the contact a circuit is closed through the previously mentioned conductor 6|, a conductor 11, a second electrical control device such as relay 18, to one of conductors 19 completing a circuit to the source of power. Relay 18 is adapted to efiect upward movement of a pair of normally open switches 80 and 8| associated therewith. One of the contacts associated with the last mentioned switch is connected by a conductor 82' to the contact 59 of switch 58. The other contact of the switch is connected by a conductor 83 to a conductor '84 leading to the cold .contact 85 of a pair'of adjustably mounted contacts 85 and 86 cooperatively associated with thermal responsive elements 81 of the heat exchanger 81 in turn is conbranch of which leads to the solenoid valve 34 and the second branch to a third electrical control device, such as the relay 90 from which conleading to the source of power. Thus, whenever switch 59 is in the position indicated, as it will be whenever the heating thermostat 9| is satislied, and switch 15 is in the position indicated, as it will be whenever the cooling thermostat 43 calls for cooling, the relay 99 will be energized through a circuit including the heat exchanger thermostat in its .cold position. The relay is adapted to effect upward m'ovement of a paircf normally open switches 92 and 93, associated therewith. Switch 93 is adapted to connect the fan motor l9 to the source of power through conductors 19. Switch 92 is adapted to close a circuit including conductor 94, the previously mentioned switch 89 and a conductor 95 to energize an electrical control device such as relay 96 connected to one of a pairof conductors 91 through which power is supplied to thecompressor motor 29 whenever switch 98 is actuated in response to energization of the relay.

The fan may be operated alone in summer time merely by closing switch 99A controlling the energization of relay 99 through a circuit including the heat exchanger thermostat in its cold position.

The humidifier control circuit extends from the source of supply through conductor 99 to the humidostat 44, and thence through conductor I99 to the normally open switch 65 associated with relay 62, and conductor IM to the solenoid winding controlling the actuation oi valve 32. cording to this arrangement the humidifier can be operated only when the heating means is in operation, the humidity within the space is below the value at which the humidostat is set to operate and the fan is in operation. The lastmentioned prerequisite is fulfilled on a call for heating when the thermostatic element 91 of the heat exchanger thermostat moves from engage ment with its -cold contact 95 into engagement with its hot contact 96, thereby closing a circuit through conductors 99, I92, and 66, switch member 58 in engagement with contact 69, and conmaintain the enclosure at a temperature of seventy degrees, and that the cooling thermostat 43 is adapted to maintain the enclosure at a temdegrees at most and therefore, as far as this de-; scription is concerned, the temperature values indicated may very well be assumed. More particularly, it will be assumed that thermal element 63 is in engagement with contact 5| at all temperaturesbelow seventy degrees and in engagement with contact 52 at all temperatures above this value. Likewise, it will be assumed that thermal element II is in engagement with contact 69 at all temperatures below degrees and mengage'ment with contact '|9 at all temperatures above this value. It will be assumed also that thermal responsive element 61 of the heat exchanger thermostat 42 will move'out of engagement with cold contact 95 and into engagement with hot contact 96 at some predetermined value, such as one hundred and twenty degrees..- 'I'he se temperatures are to be considered merely asillustrative and in no way to limit the scopeofmy in vention.

2 Considering first the operation or the tern when the temperature within the enclosure is below a value of seventy degrees, then it will be seen that the relay 13 associated with the cooling thermostat is energized because element ll is in engagement with'contact 69. The energizing circuit for this relay extends from the secondary winding of the transformer through conductor 61, contact 69, element 'II in engagement therewith, and conductor 12 to the relay winding and thence to the other side of the transformer winding. Energization of the relay eifects upward movement of switches .14 and I5, switch 14 closing a holding circuit for the relay and switch 15 being moved out of engagement with contact 16 to de-energize relay I9.

When the temperature within the enclosure is below seventy degrees, relay 55 associated with the heating thermostat ll is also energized. The energizing circuit extends from the secondary winding of-the transformer through conductor 49, contact 5|, thermal responsive element 53 in engagement therewith, and conductor 54 to the relay winding and thence to the other terminal of the transformer winding. Energization of the relay eflects upward movement of its associated switches 56 and 59, the former closing a holding circuit for the relay and the latter energizing control device 62 controlling the operation of the heatincreasing means.

The energizing circuit for relay 62 extends from the source of power through conductor 6|, switch 59 inengagement with contact 69, conductor 66, to the relay winding and thence through one of conductors 63 to the other conductor of the source of energy. Energization of the relay 62 effects upward movement of switch 64 and resultant. energization of thefurnace controlling means 39.

Initiation of operation'of the furnace results in the transfer of heat therefrom to the heat exchange coil 35 within the conditioner. Thus far the fan has not been placed in operation but after the temperature surrounding the heat exchanger thermostat'rises to a value above one hundred and twenty degrees, the fan will be renr .dered operative when thermal element 91 engages its associated hot contact 66 and closes an energizing circuit for the fan control relay 99. This circuit extends from the source of power through conductor 6|, switch 59 in engagement with contact. 69, conductor66, conductor I92, contact 96,

element 81 inengagement therewith, conductors 99 and 99 to the relay winding and thence through conductor 9| and one of the pair of conductors 19 back to the source of power. Energi-' zation of the relay effects upward movement of switches 92 and 93. Operation of thefirst mentioned switch'has no'eflect on-the system because of the fact thatswitch 99 is in its open position.

However, operation of switch 93 results in the en ergization of fan motor l9 through conductors l9 and circulation of air through the enclosure by fan l9. Thus, on a call for heat by ,the heating thermostat II, the heating meansis set into operation and thereafter whenthe temperature of the air'adjacent the .heat exchanger thermostat reaches a predetermined value the air circulating means is placed intooperation...

Humidification is desirable particularly during the heating season and provision is made in the conductor;til,thermal responsive element81 in ,instant control system tor such operation. En-

ergizationof theheating control relay. 62' not only effects operation of the heating apparatus but 'als'o oohditiohs thef-humidifier control circuit through-"closure' of switch 65 and the resultant operation of the heat exchanger thercontrolling fthe first"c181v'mter to the humidifier through a circuitextendi'n'g' from the source 45 ,58 andcontact G9. Engagement of contact '59 ib'ythe switch 58 does not effect any operation at through conductor 99 ,*humidostat 44, conductor 1 i101 switch "55 in its closed osition, conductor 'I 0 l,1to the solenoid winding, and thence through engagement with contact 86,-conductors I82 and '55, 'contact; Bland switch arm 58 in engagement therewith, and conductor 6| back to the source.

'I'hehumidifyingfunction is terminated whenever the humidity again rises above the value for which the humidostat is calibrated andifalso hene ver the temperature requirements within the enclosure Ill have been met. I When",'the temperature within the enclosure rises above seventy degreesthe thermal responsive element 53 will engage contact 52 and thereby short circuit relay 55 in an obvious manner. Switches 56 and 58 are thereby moved, downwardly the former opening a previously described holding: circuit and the' latter engaging contact 59. Operation of the "heating means as well as ofQthe humidifying means, if the latter was in operation at "this time, is terminated by the opening of the circuit "between switch member jthistime'beoause of the fact that relay 18 is Qde-energizedand switch 8| consequently open.

falls belowseventy degrees the above described operationwfll be repeated.

if the temperaturewithin the enclosure l0 again mal responsive element H of the cooling thermostat w1ll engagecontact 10 and thereby short circuit relay 19 andde-energize it. This de-en- 'ergization results in the downward movement 01 switch arms 14 and 15, the former opening the holding-circuit for the relay l3 and the latter effecting energization of relay 18. The latter in turn. effects, through operation of switches 80 and-8|, the energizationof the fan control relay 98 and the cooling control relay 95. '1'ne energizing circuit for relay. [8 extends from the source of power through conductor 6|, switch 15 A in engagement-with contact 16, conductor 11 to the relay winding and; from thence through one o1 conductors 19 to the source of power. Switches 1 respective circuitfi, the'former conditioning a cir- 88and 8| are moved gupwardly to close their cuit leadingQfromconductor 94 through'conductor, 9,5 to the cooling control relay 96 whereby.

..the latter will be energized upon energization of relay 90 and the r'esultingclosure thereby of switch 92. ,Switch ,8l energizes fan control re lay-9t, through aci'rcuit' extending from the source of power toconductor 8|, switch 58in engagement with contact 59, conductor 92, switch 8] in its closed: position, 1 conductors '88,

, Q'Ifthe temperature conditions without the encontact 85 and element 81 in engagement therewith, and conductors 8,8 .and 89 to the-relay and thence through conductor ,8! and one of; .conductors 19 back. to, thegsource,

It should be noted that; the above describ d energizing circuit extends, through element 81in engagement with its; cold contacts AIter termination of operation ofxthe heating meansthe heat exchangeri thermostat returns-to its, cold position very shortly thereafter because,v of 1 the fact that it returns to engagementwiththecold the latter connecting motoralllto the source of,

power and the former completing the energizing vcircuit for the cooling controlrelay -96. The complete energizing circuit for ;relay'95 extends vfrom the source of power through conductor,

switch 58 in engagement with contact 59,, conductor 82, switch 8|, conductor 83, switch 92 in its closed position, conductor 94, switch 8|! and conductor 95 to the relaywindlng and thence through one of conductors 9|.back to the source.

Energization of the cooling control relay ef fects upward movement of switch 98 and the latter thereupon connects compressor motor 29 to thesource of energy through'conductors 91. Motor 29 operates the compressor 22 of the'cooling apparatus and the refrigerant flowing through-evaporator 20 cools theair flowing therei by. After a. length of time determined by outdoor temperature conditions, the temperature within the enclosure decreases below eighty degrees. Thereupon thermal responsive element] I engages contacts-69 and the previously-described energizing circuit for relay 13 is closed.- Switches H and 15 are moved upwardly, the former closing a holding circuit for the relay and the latter de-energizing relay 18. De-energization of the.

last mentioned relay terminates operation of both the cooling apparatus and fan by opening switches 80 and8l.

As long as the room to operate in the assumed ranges, the two will cooperate in the manner described to control the heating and cooling appartus. If thefthermostats were entirely independent of each other in accordance with past practice and the twovwere accidentally adjusted to operate'within the same temperature range, then both the heating and cooling apparatus would be operated simultaneously, with obvious'deleterious eflects., Such op eration is not possible with the above described control because of the fact that the cooling thermostat can take control only when the heating thermostat is in its off position, i. e., when switch 58 is in engagement with contact 59. From the above described operation it will be seen that the fan and cooling control relays 98 and 96 cannot possibly be energized'unless switch '58 is in engagement with'contact 59.- Thus, it the two thermostats were adjusted to operate within the same rangethe cooling thermostat could not exertits control function unless the,

temperature within thev enclosure ID was. above the value at which the heating "thermostat calls forheatp 1 It should be noted assimilate ans, operated intermittently during both "heating and cooling- During heating the fan is placedv into operation upon a call for 'heat by the heating thermostat and when the heat exchangerthermostat has been actuated to its hot position. and immediate thermostats are adjusted culation alone will impart a certain cooling eflect to persons within the enclosure. By use of the heat exchanger thermostat during the heating operation I prevent the discharge of cold air into the room upon a call for heat.

What I claim as new and desire to secure by Letters Patent of the United States is: v

1. In an air conditioning system, the combination including heating means and cooling means for an enclosure, thermal responsive means responsive to the temperature of said heating means, means controlling said heating means including a thermal responsive device responsive to the temperature of said enclosure and adjustable to operate at a selected temperature, means controlling said cooling means including a thermal responsive device responsive to the temperature of said enclosure and adjustable to operate at a second selected temperature normally diflerent from said first mentioned temperature of said enclosure, and means controlled jointly by said first and second mentioned thermal responsive devices for rendering said last mentioned thermal responsive device ineilfective' to control said cooling means when the two ad- .iustable thermal responsive devices are adjusted to operate at the same temperature.

2. In an air conditioning system, the combination including heating means and cooling means for an enclosure, means controlling said heating means including a thermostat adjustable to operate at a selected temperature, means controlling said cooling means including a thermostat adjustable to operate at a second selected temperature normally diflerent from saidfirst mentioned temperature, and means including a thermostat responsive to the temperature of said heating means for rendering said last mentioned control means eilective to control said cooling means only when said first mentioned control means has reduced the temperature of said heating means below a predetermined value.

3. In an air conditioning system, the combination including, air circulating means, air heating means and air cooling means for an enclo-" sure, means including an adjustable thermostat responsive to the temperature of the enclosure and .controlling said heating means for maintaining the temperature within said enclosure within predetermined limits, means including an adjustable thermostat responsiveto the temperature of the enclosure and controlling said cooling means for maintaining the temperature within said enclosure within Fredetermined limits and normally adjusted to operate without said first mentioned limits, a thermostat responsive to the temperature 01' said heating means and interconnected with said heating control means for operating said air circulati'ngmeans when the temperature of the air heating means is above a predetermined value and interconnected with said cooling control means for operating said air circulating means when the temperature of said heating means is below" said value and means including. said last mentioned thermostat for rendering said heating. control means solely efl'ective when both said adjustable thermostats are adjusted to exert predetermined control functions within the same limits.

4. In an air conditioning system the combination including means for circulating air to an said cooling control means-for operating said air circulatingmeans when the temperature of said heating means is below said value and means controlled by said heating thermostat for preventing said cooling thermostat .from rendering said cooling means effective when both said thermostats are adjusted to exert control within the same limits.

5. In a temperature regulating system, the combination including heating means, cooling means, electrical control means for each, means including a source of energy and thermal responsive means having a two position relay controlled thereby and adapted in one position thereof to connect the heating control means to said source of energy for controlling the operation of said heating means, a thermostatic switch responsive to the temperature of said heating means and having an energizing circuit for said cooling control means adapted to be connected to said source of energy by said relay in the other position thereof, second thermal responsive means, and relay means controlled thereby adapted selectively to complete said energizing circuit for controlling the operation of said cooling means.

6. In a. conditioning system for an enclosed space, means for circulating a conditioning medium through said space, means for heating said medium, means for cooling said medium, thermal responsive means in said.- space and having electroresponsive switch mechanism controlled thereby for controlling said cooling means .to maint'ain'the space temperature within predetermined limits, second thermal responsive means in said space having electroresponsive switch mechanism controlled thereby for controlling said heating means to maintain the space temperature within other predetermined limits, thirdthermal responsive means located adjacent said heating means having electroresponsive switch mechanism controlled thereby and interconnected with the electroresponsive switch mechanism controlled by said first and second thermal responsive means for controlling the operation of said circulating means, and interlocking circuit connections between said electroresp'onsive switch mechanisms whereby said first mentioned thermal responsive means is prevented from controlling electroresponsive switch mechanism for the cooling means when the second space having a in other predetermined limits, third thermal responsive means located adjacent the heating means and having a relay for controlling operation of said circulating means, and interlocking connections between said relays whereby the circulating means is controlled jointly by the second and third mentioned relays when the heating means is placed into operation and jointly by the first, second and third mentioned relays when the cooling means is placed in operation.

8. In a conditioning system for an enclosed space, the combination including means for circulating a conditioning medium through said space, means for heating said medium, means for cooling said medium, electrical control means adapted-when energized to render said heating means operative, second electrical control means adapted when energized to render said cooling means operative, third electrical control means I adapted when energized to render said circulating means operative, a source of electrical energy, an energizing circuit for said first mentioned control means, and thermal responsive means in said space having a relay for connecting said energizing circuit to said source, an energizing circuit for said third control means including said relay and a second thermal responsive means adjacent said heating means and having a relay so connected that the circulating means is rendered operative only upon a call for heat by said first mentioned thermal responsive means and when the temperature of the medium is above a predetermined value, and an energizing circuit for said second control means including said first and second mentioned relays, and a third thermal responsive means in the space having a relay so connected with said first and second mentioned relays that the third mentioned relay is efiective to energize said second electrical control means to render the cooling means operative only when operation of said heating means is stopped by the first mentioned thermal responsive means.

9. In a conditioning system for an enclosed space, the combination including means for circulating a conditioning medium through said space, means for heating said medium, means for cooling said medium, electrical control means adapted when energized to render said ,heating means operative, second electrical control means adapted when energized to render said cooling v means operative, third electrical control means adapted when energized to render said circulating means operative, a source of electrical energy,

, an energizing circuit for said first" mentioned adjacent said heating control means, and thermal responsive means in saidspace having a relay for connecting said energizing circuit to said source, an energizing circuit for said third control mearis including said relay and a second thermal responsive means means so connected that the circulating means is rendered operative only upon a call for heat by said: first mentioned thermal responsive means and when the temperature of the medium is above a predetermined value, and an energizing circuit for said second control means including said relay, a third thermal responsive means positioned in said space, and a pair of relays actuatable thereby, all so connected that the latter are efiective when actuated to energize said circuit to render said cooling means operative only when the first menrelay for controlling said heating means to maintain said space temperature withof said relays also effecting energization of the third control means to place the circulating means in operation.

10. In a room temperature regulating system,- the combination including a heat transfer medium circulating means, heating means, cooling means, an electrical control device for each adapted when energized to render the corresponding means efl'ective, a first and second thermal responsive means, each responsive to a difierent room temperature, a third thermal responsive means operable in response to a temperature condition of the heat transfer medium, and interlocking relay connections whereby the first thermal responsive means separately controls the energization of the electrical control device for the heating means and jointly with the second thermal responsive means controls the energization of the electrical control device for the circulating means when the heating means is in operation and jointly with the second and third thermal responsive means controls the energization of the electrical control device for the cooling "means and the circulating means when the operation of the heating means is stopped.

11. In an air conditioning system for an enclosure, the combination includingmeans for circulating air to the enclosure, means for heating the air, means for cooling the air, electrical control means for each, a pair of adjustable thermostats responsive to the air temperature within the enclosure and normally adjusted to operate at different temperature values, a separate thermostat responsive to-the temperature of the airadjacent said air heating means, and interlocking relay connections between said thermostats whereby one of said pair of thermostats separately controls the energization of the electrical control means for the heating means and jointly with said separate thermostat controls circulating means, heating means for said medium, cooling means for said medium, electrical operating means for each, means including a pair of thermal responsive means responsive to different temperatures of the heat transfer medium, and electrical circuit connections controlled separately by one of said thermal responsive means for selectively energizing and deenergizing the heating means, cooperating circuit connections ,controll'ed jointly by said pair of thermal responsive means for selectively energizing and deenergizing the heating medium circulating means, and means including a third thermal responsive means responsive to the temperature ofsaid heating means, and circuit connections jointly controlled by said pair of thermal responsive means for rendering said third thermal responsive means effective to selectively energize the cooling and circulating means only when the heating means is deenergized.

13. In a temperature regulating system, combination including a heat transfer medium circulating means, heating means for said medium, cooling means for said medium, control means therefor including a pair of thermal re- 10 the sponsive means, one for separately controlling the operation of said heating means and jointly with the other controlling the operation of said circulating means, and means including a third thermal responsive means responsive to the temperature of said heating means and having interlocking connections with said pair of thermal responsive means for controlling said cooling means and said circulating means only when the opera.- tion of said heating means-is stopped.

HARRY R. CRAGO. 

